1. Field of the Invention
The present invention relates to an apparatus for controlling the injection quantity of pulverized coal, which is installed in a system for injecting pulverized coal into a blast furnace.
2. Description of the Related Art
For a pulverized coal injection system to a blast furnace, there are known the following methods for controlling the quantity of pulverized coal injected from a pressurized vessel (that is, a feed tank) (refer to Japanese Patent Publication Nos. 51-29684, 58-23301, 59-34605, 3-21454, and Japanese Patent Application Laid-Open No. 59-213434).
(1) Method of controlling the injection quantity of pulverized coal by regulating the pressure in the feed tank
In this method, a signal corresponding to the weight of pulverized coal measured by a load cell attached to a feed tank is differentiated with respect to time to calculate the injection rate of pulverized coal from the feed tank, and the internal pressure of the feed tank is regulated so that the injection rate becomes a prescribed rate, thereby to control the injection quantity of pulverized coal.
FIG. 1 is a schematic diagram illustrating the configuration of an apparatus implementing this method. In the figure, chain lines indicate signal flows. The reference numeral 1 designates an equalizing tank for temporarily storing pulverized coal and supplying it under pressure to a feed tank 2. The feed tank 2 is provided with a load cell 5 for measuring the weight of pulverized coal in the feed tank 2. Connected to the load cell 5 is a powder weight indicating controller 16. A signal of the injection rate of the pulverized coal from the powder weight indicating controller 16, a signal of the internal pressure of a powder conveying pipe 8, and a signal of the internal pressure of the feed tank 2 are fed to a differential pressure indicating controller 7, which regulates the internal pressure of the feed tank 2 by detecting the difference in internal pressure between the feed tank 2 and the powder conveying pipe 8.
The following describes the operation for controlling the injection quantity of pulverized coal according to this method.
When the weight of pulverized coal in the feed tank 2 is measured by the load cell 5, the signal of the measured weight is fed to the powder weight indicating controller 16 which then differentiates the signal of the measured weight with respect to time to calculate the injection rate of the pulverized coal and controls the differential pressure indicating controller 7 so that the injection rate is maintained at the prescribed rate. The differential pressure indicating controller 7 controls the internal pressure of the feed tank 2 by introducing a pressurizing gas into the feed tank 2 so that the difference in the internal pressure between the feed tank 2 and the powder conveying pipe 8 becomes the differential pressure corresponding to a predetermined injection rate of the pulverized coal.
(2) Method of controlling the injection quantity of pulverized coal by regulating the rotational speed of a rotary feeder
(2.1) A signal corresponding to the weight of pulverized coal measured by a load cell attached to a feed tank is differentiated with respect to time to calculate the injection rate of pulverized coal from the feed tank, and the rotational speed of a rotary feeder is regulated so that the injection rate becomes a prescribed rate, thereby to control the injection quantity of pulverized coal.
FIG. 2 is a schematic diagram illustrating the configuration of an apparatus implementing this method. A feed tank 2 is provided with a load cell 5 for measuring the weight of the pulverized coal in the feed tank 2, and a rotary feeder 15 is installed in a lower outlet of the feed tank 2. A signal of the weight from the load cell 5 is fed to a powder weight indicating controller 16 which then supplies a control signal to the rotary feeder 15.
The following describes the operation for controlling the injection quantity of pulverized coal according to this method.
When the weight of pulverized coal in the feed tank 2 is measured by the load cell 5, the signal of the measured weight is fed to the powder weight indicating controller 16 which then differentiates the signal of the measured weight with respect to time to calculate the injection rate of the pulverized coal and controls the rotational speed of the rotary feeder 15 so that the injection rate is maintained at a prescribed value.
(2.2) From the flow rate of pulverized coal measured by a powder flow meter installed in a powder conveying pipe, the injection rate of pulverized coal from a feed tank is calculated, and the rotational speed of a rotary feeder is regulated so that the injection rate becomes a prescribed rate, thereby to control the injection quantity of pulverized coal.
FIG. 3 is a schematic diagram illustrating the configuration of an apparatus implementing this method. As shown, a rotary feeder 15 is installed in a lower outlet of a feed tank 2, while a powder flow meter 4 is installed in a powder conveying pipe 8. A measurement signal issued from the powder flow meter 4 is fed to a powder flow indicating controller 6 which then supplies a control signal to a rotary feeder 15.
The following describes the operation for controlling the injection quantity of pulverized coal according to this method.
When the flow rate of pulverized coal flowing through the powder conveying pipe 8 is measured by the powder flow meter 4, a signal of the measured flow rate is fed to the powder flow indicating controller 6 which then calculates the injection rate of the pulverized coal on the basis of the signal of the measured flow rate and controls the rotational speed of the rotary feeder 15 so that the injection rate is maintained at a prescribed value.
Problems in the above prior art methods of controlling the injection quantity will now be described.
Method (1) has the following problems.
(a) Since the injection rate of pulverized coal from the feed tank 2 is calculated by differentiating the signal measured by the load cell 5 attached to the feed tank 2, the obtaining of data on the injection rate is delayed by the calculation time which depends on the change in the weight of pulverized coal in the feed tank 2, resulting in slow control response.
(b) During pulverized coal being supplied into the feed tank 2 from the equalizing tank 1, the injection rate of the pulverized coal from the feed tank 2 cannot be calculated, since the detection of the change in the weight of the injected pulverized coal is impossible.
(c) Since the injection rate of the pulverized coal from the feed tank 2 is only controlled by regulating the pressure in the feed tank 2, fine adjustment of the control is not possible, and also, the response speed is slow.
Method (2.1) in (2) has the following problems.
(a) Since, the injection rate of pulverized coal from the feed tank 2 is calculated by differentiating the signal given from the load cell 5 like in the method (1), the control response is slow.
(b) During pulverized coal being supplied into the feed tank 2 from the equalizing tank 1, the injection rate of the pulverized coal from the feed tank 2 cannot be calculated like in the method (1).
(c) Although the rotary feeder is capable of fine adjustment of the injection rate of pulverized coal from the feed tank 2, the injection rate of pulverized coal per one rotary feeder is limited, and it is extremely difficult to increase the injection capacity of the rotary feeder; therefore, the only way to handle a large injection quantity is to increase the number of rotary feeders to be installed.
(d) Owing to the inherent construction of the rotary feeder, pulsation occurs in the injection of the pulverized coal from the feed tank 2, which disturbs continuity of the injection.
Method (2.2) in (2) has the following problems.
(a) Like in the method (2.1), although the rotary feeder is capable of fine adjustment of the injection rate of pulverized coal from the feed tank 2, the injection rate of pulverized coal per one rotary feeder is limited, therefore, the only way to handle a large injection quantity is to increase the number of rotary feeders to be installed.
(b) Like in the method (2.1), owing to the inherent construction of the rotary feeder, pulsation occurs in the injection of pulverized coal from the feed tank 2, which disturbs continuity of the injection.
(c) According to the above-mentioned problem (b), accuracy in the measurement by the powder flow meter 4 of pulverized coal passing through the powder conveying pipe 8 lowers. Therefore, accuracy in the calculation of the injection rate of pulverized coal lowers, thereby making the control itself of the injection rate of the pulverized coal unstable.
The above and further objects and features of the invention will more fully be apparent from the following detailed description with accompanying drawings.